It is reported that there are over 10,000 patients with refractory pancreatic cancer in Japan, the occurrence thereof is increasing year after year, and it is assumed that the number of patients will continue to increase. Even if pancreatic cancer were surgically removed, small cancer cells have often infiltrated and metastasized to other organs. Accordingly, pancreatic cancer often relapses, and the 5-year survival rate is as low as 9%; that is, the prognosis of pancreatic cancer is very poor. For the purpose of preventing postoperative recurrence, Gemcitabine, an anticancer agent, has been employed. However, the primary purpose of Gemcitabine administration is pain relief, and tumor size reduction or survival advantage can hardly be expected. At some hospitals, another anti-cancer agent, TS-1, which is currently used for gastric cancer, is used, although it is difficult to expect any therapeutic effects.
In order to improve the prognosis for pancreatic cancer, early detection is important, as it is with other cancers; however, early detection is difficult because pancreatic cancer shows substantially no initial symptoms. To date, methods of detecting pancreatic cancer using carcinoembryonic antigen (CEA) and glycoproteins (CA19-9 and Dupan-2) in biological samples as tumor markers of pancreatic cancer have been actively employed. However, the levels of such tumor markers do not become elevated unless pancreatic cancer advances, and such markers occasionally show normal values in the progressive stage. Accordingly, such tumor markers are not considered to be sufficient for accurate detection of pancreatic cancer. In addition, most tumor markers that are currently known are present in very small amounts in the body fluids (at the pg/ml level). In order to detect such small amounts of markers, accordingly, detection techniques with high sensitivity or special techniques are necessary. Under such circumstances, a novel technique for detecting pancreatic cancer in a simple manner with high sensitivity is expected to be applicable to diagnosis of pancreatic cancer. It is necessary to undergo periodic thorough examinations in order to detect early-stage pancreatic cancer. Accordingly, a method of detecting cancer that can be carried out in a simple manner with the use of blood serum or urine samples without the imposition of physical or financial burdens on either healthy individuals without pancreatic cancer or patients with cancer has been awaited.
Also, pancreatic cancer is refractory in dogs. Although a lump can be observed in the abdominal region of a dog afflicted with pancreatic cancer, the major symptoms are rapid energy loss, unsteady gait, and gait abnormalities resulting from hypoglycemia. In most cases, the development of cancer would not be detected until such symptoms are observed. In addition, pancreatic cancer is often likely already to be in the advanced stage when such symptoms are observed. In addition to surgical removal of pancreatic cancer, accordingly, therapeutic techniques are limited to supportive therapy and administration of anticancer agents. As with the case of human patients, early detection is important for dogs afflicted with pancreatic cancer in order to effectively treat such pancreatic cancer. As with the case for humans, there were no diagnostic agents for dogs in the past that allowed detection of pancreatic cancer at the early stage in a simple manner. In the field of veterinary medicine, detection techniques such as radiographic techniques by means of X-rays, CT, or MRI have not yet become common. At present, detection is carried out by palpation, simple blood testing, and X-ray photography, and diagnosis is heavily dependent on the experience of veterinary doctors. If a simple means for cancer detection with high sensitivity that can be applied to diagnosis of pancreatic cancer in dogs is provided, adequate treatment can be performed, which has great advantages for dog owners and veterinary doctors.
Cytoplasmic- and proliferation-associated protein 1 (CAPRIN-1) is an intracellular protein that is expressed when normal cells in the resting phase are activated or undergo cell division. CAPRIN-1 is also known to be involved in the control of the transport and translation of mRNAs through formation of cytoplasmic stress granules and RNA in a cell. Also, genes encoding CAPRIN-1 proteins are demonstrated to be expressed specifically in canine and human testis and malignant tumor cells, FCM analysis of breast cancer cells with the use of antibodies against CAPRIN-1 demonstrates CAPRIN-1 expression on the surfaces of breast cancer cells, and immunohistochemical staining using breast cancer tissues demonstrates CAPRIN-1 expression at high level in breast cancer cells. In addition, it has been reported that the antibodies mentioned above would damage breast cancer cells through the functions of lymphocytes, and that antibodies against CAPRIN-1 exert potent antitumor effects in cancer-carrying mouse models into which breast cancer cells had been transplanted (Patent Literature 1). Also, it has been reported that cancers such as breast cancer could be diagnosed by measuring either antibodies induced in the body of a subject against CAPRIN-1 present in the blood serum or polypeptides that undergo antigen-antibody reactions with CAPRIN-1 (Patent Literature 2). Up to the present, however, there have been no reports of the fact that pancreatic cancer can be diagnosed by measuring either antibodies against CAPRIN-1 induced in the blood serum of a patient with pancreatic cancer or polypeptides that undergo antigen-antibody reactions with the CAPRIN-1.